Author Topic: vacuum fluorescent display  (Read 474 times)

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Offline veedub565

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vacuum fluorescent display
« on: October 14, 2019, 06:28:21 pm »
Hi, I have an old piece of test equipment (TTC Fireberd 6000A) with a vacuum fluorescent display. I noticed that with the unit powered up, some of the segments are dimly lit, even though they are not displaying anything.

 I'm not too familiar with this type of display, I've read on another post that it could be a failing display driver. Any thoughts ?

Picture attached
 

Offline veedub565

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Re: vacuum fluorescent display
« Reply #1 on: October 14, 2019, 06:49:22 pm »
Just to add, the rest of the display does not appear especially dim. And oddly some segments appear super bright. Additional picture attached
 

Offline mzacharias

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Re: vacuum fluorescent display
« Reply #2 on: October 16, 2019, 04:57:12 pm »
I would definitely suggest checking power supply voltages. Might get lucky. Typically 6-10 volts AC for the filaments and -30V dc for the main display, probably 5 volts for the driver IC. It's doubtful this is a "chip on glass" type, but you can tell if only about 1/3 of the available pins are used and the rest cut short to the glass. (the ones I've seen, anyhow)
 

Offline PKTKS

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Re: vacuum fluorescent display
« Reply #3 on: October 16, 2019, 05:10:45 pm »
As said above the voltages are first priority.

VFDs are regular TUBES - yes indeed valves...

But a VFD this size should have a complete integrated controller
underneath. Voltages for cathode and grid are very tricky to setup
and being integrated if just one failed .. the whole chip is replaced.

Lucky or not there are know replacements being Noritake the top manf.
Compatible list is very short.

And they age... like any regular tube they just got used..

Need to find out the numbers printed on the assy
and  verify if the malfunction is really a faulty chip

Paul
« Last Edit: October 20, 2019, 10:04:19 am by PKTKS »
 

Offline dom0

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Re: vacuum fluorescent display
« Reply #4 on: October 16, 2019, 08:04:34 pm »
Kinda looks like ghosting, so there might be a problem in the filament driving or how the filament voltage is biased relative to the rest of the circuit.

Super bright segments indicates that possibly the multiplexing is not working quite right. Perhaps a barely working oscillator providing a rather irregular clock to the VFD driver IC?
,
 

Offline veedub565

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Re: vacuum fluorescent display
« Reply #5 on: October 19, 2019, 07:57:08 pm »
Sorry for the late reply to this, the display is model CU40026SCPB-T21a

Looks like there are controller chips on the back of the assy. If I can find a datasheet I'll start prodding about and check some voltages.
 

Offline PKTKS

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Re: vacuum fluorescent display
« Reply #6 on: October 20, 2019, 10:06:25 am »
These fully integrated modules can be replaced as a whole.

Depending on price and options it may be even better solution
 


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